Subject: "permission denied to COPY to or from an external program" even with GRANT pg_execute_server_program

From: Chema <[email-masked]>
Date: Wed, 12 Jun 2024 19:31:32 -0600

Dear Postgreezers,

been banging my head against this one for a couple days.  Googling and
StackExchange were just as useful, so you're my last hope.  I've been
unable to get a non-admin user to run Copy From Program even after granting
pg_execute_server_program, and everything else I could think of.  It always
fails with ERROR: permission denied to COPY to or from an external program.

I'll let the code speak by itself.  Here's a minimal example that I've
tried in the last official Docker image:

-- Spin a temporal Pg and connect to psql

--docker run --name pg16 -e POSTGRES_PASSWORD=qwer -d postgres:16

--docker exec -ti pg16 psql -U postgres

CREATE TABLE testtable (

id int NOT NULL GENERATED ALWAYS AS IDENTITY,

name text NOT NULL

);

Create Role justintestin noinherit login password 'qwer';

-- Necessary privileges

GRANT CONNECT ON DATABASE postgres TO justintestin;

GRANT USAGE ON SCHEMA public TO justintestin;

GRANT ALL ON ALL TABLES IN SCHEMA public TO justintestin;

-- Apply them to new tables/views created by admin account

ALTER DEFAULT IN SCHEMA public GRANT ALL ON TABLES TO justintestin;

-- Allow Copy From Program... or try to anyway

GRANT pg_execute_server_program TO justintestin;

-- Tests

GRANT ALL ON testtable TO justintestin;

GRANT ALL ON SCHEMA public TO justintestin;

GRANT ALL ON DATABASE postgres to justintestin;

GRANT pg_read_all_data TO justintestin;

GRANT pg_write_all_data TO justintestin;

--Copy works with admin account

Copy testtable(name) From Program 'echo "Buffa Testata"' CSV;

-- COPY 1

--But fails with justintestin

SET role justintestin;

Copy testtable(name) From Program 'echo "Errato Denegato"' CSV;

--SQL Error [42501]: ERROR: permission denied to COPY to or from an
external program

-- Detail: Only roles with privileges of the "pg_execute_server_program"
role may COPY to or from an external program.

--Even tho he's privileged

SELECT rolname FROM pg_roles WHERE

pg_has_role(current_user, oid, 'member');

-- rolname

---------------------------

-- pg_read_all_data

-- pg_write_all_data

-- pg_execute_server_program

-- justintestin

--Insert works

Insert Into testtable ("name") VALUES('Pazzo Intestinato');

--INSERT 0 1

Select * From testtable;

SELECT current_user, session_user;

-- Clean up for new test

SET role postgres;

Drop Table testtable;

Drop Owned By justintestin;

Drop Role justintestin;

What am I missing? (besides a few chunks of hair)

---

From: "David G. Johnston" <[email-masked]>
Date: Wed, 12 Jun 2024 18:44:40 -0700

> GRANT pg_execute_server_program TO justintestin;
Pretty sure since you choose not to allow justintestin to inherit stuff you
will need to issue a “set role to pg_execute_server_program” before you
attempt the copy command.

David J.

---

From: Tom Lane <[email-masked]>
Date: Wed, 12 Jun 2024 21:48:06 -0400

> fails with ERROR: permission denied to COPY to or from an external program.

Works for me:

regression=# create user joe;
CREATE ROLE
regression=# \c - joe
You are now connected to database "regression" as user "joe".
regression=> create table jt (t1 text);
CREATE TABLE
regression=> copy jt From Program 'echo "Buffa Testata"' CSV;
ERROR:  permission denied to COPY to or from an external program
DETAIL:  Only roles with privileges of the "pg_execute_server_program" role may COPY to or from an external program.
HINT:  Anyone can COPY to stdout or from stdin. psql's \copy command also works for anyone.
regression=> \c - postgres
You are now connected to database "regression" as user "postgres".
regression=# GRANT pg_execute_server_program TO joe;
GRANT ROLE
regression=# \c - joe
You are now connected to database "regression" as user "joe".
regression=> copy jt From Program 'echo "Buffa Testata"' CSV;
COPY 1

What PG version are you working with?

			regards, tom lane

---

From: Chema <[email-masked]>
Date: Wed, 12 Jun 2024 19:53:43 -0600

>
>
> Pretty sure since you choose not to allow justintestin to inherit stuff
> you will need to issue a “set role to pg_execute_server_program” before you

That was it!  Blind paranoia bites my rear again.  Thanks!